1. Field of the Invention
The present invention relates to a threshold voltage control apparatus, a test apparatus, and a circuit device. The present invention particularly relates to a threshold voltage control apparatus for adjusting timing of a threshold voltage at user's discretion to be supplied to a comparator.
2. Related Art
Generally, in case of testing a device under test (DUT) such as a semiconductor circuit, a method of inputting a predetermined signal into the DUT, measuring an output signal from the DUT, and determining PASS/FAIL of the DUT is known. For example, by inputting a predetermined logic pattern into the DUT and determining whether a logic pattern of the output from the DUT matches an expected pattern, it is possible to test whether the DUT operation is good or bad.
In case of doing such a test, an output of the DUT is inputted into a test apparatus. However, in case of this signal being attenuated through a path for transmitting the signal from the DUT to the test apparatus, a logic pattern to be inputted into the test apparatus and a logic pattern actually outputted from the DUT may be different.
In order to solve a problem like this, a test apparatus generally has a function in its input section to correct a waveform of an output signal from a DUT corresponding to signal attenuation in a transmission path. For example, a front end of an input section of a test apparatus includes a filter circuit to emphasize high frequency components, to correct for signal attenuation through the transmission line.
However, a typical test apparatus can emphasize high frequency based on a timing of an edge of the output signal from the DUT, it was not possible to correct an output waveform from the DUT on a timing at user's discretion. For example it was not possible in advance to correct for reflected waves generated in phase away from an edge in time wise. In addition, depending on a specification of the output section of the DUT or a specification of the transmission line of the test apparatus, parameters for the filter circuit for emphasizing high frequency components needed to be modified.
For this reason, there have been cases where it was not possible to test a DUT accurately.
Also, it may have been conceived that corresponding to signal attenuation, a threshold voltage to be applied to a comparator of a test apparatus may be controlled, even in such a condition, a reflected wave which was generated in phase away from an edge in time wise, the threshold voltage could not be controlled.